I changed my timing chain and gears on my 1993 Altima GXE at 96,000 miles due to a rattling sound on top of the engine near the oil fill hole on the valve cover. I am still getting the rattling sound at 144,000 miles. Car uses no oil, still does 30mpg highway, makes good smooth power under acceleration and at speed. Howevever Idle hunts a little. The new timing chain kit was installed with one or two less chain tensionser per a service bulletin. The rattle dissapears at higher RPM's.

I am wondering if I have a worn shim, collapsing lifter, bad knock sensor, bad cam or ?

Thanks

Check the valves maybe? I have a knocking too and it's one of my valves i think.